I couldn't find a better way to validate that something is a promise.  Found this approach on stackoverflow from here:

http://stackoverflow.com/questions/14690082/how-to-check-if-a-value-is-a-promise

I didn't see anything in previous code which tried to validate that an object is a promise.

I agree that this could be problematic if the implementation of promise were to change later.  I can pull out all of the code which validates the promise.